Feedwater heater and strainer arrangement for multiple-effect thin film desalination plant

ABSTRACT

A vertical double fluted tube evaporator for water desalination has multiple closely-coupled effects with individual feedwater heaters in each effect. Feedwater manifolds in each effect supply feedwater to double fluted tubes through individual porcelain spray nozzles providing thin films on the tubes. The feedwater heaters are fed in series through each effect, while parallel branch lines supply the manifolds via in-line strainers with provisions for blow-down during normal operation if strainer blockage occurs.

mamas: I 2 She ets-Sheet 1 E. R. WEAVER PEEDWATEB HEATER AND STRAINER ARRANGEMENT F0 MU IN FILM DESALINATION PLAN Filed Dec. 14, 1970 LTIPLE-EFFECT TH HIS ATTORNEY.

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S'CONDENSATE Oct. 10, 1972 s. R. WEAVER FBEDWATER HEATER AN MULTIPLC'DPPDCT TH D STRAINER ARRANGEMENT F0 IN FILM DESALINATION PLANT Filed Dec. 14, 1970 2 Sheets-Sheet 2 LIQUID Q LEVEL FIG.4

B LOWDOWN VALVE lN'JENTORI EARLE R WEAVER, BY -6- M HIS ATTORNEY.

United States Patent O FEEDWATER HEATER AND STRAINER AR- RANGEMENT FOR MULTIPLE-EFFECT THIN FILM DESALINATION PLANT Earle R. Weaver, Topsfield, Mass., assignor to General Electric Company Filed Dec. 14, 1970, Ser. No. 97,729 Int. Cl. B01d 1/26, 3/00, 3/02, 3/08, 3/28, 21/24 U.S. Cl. 202-174 7 Claims ABSTRACT OF THE DISCLOSURE A vertical double fluted tube evaporator for water desalination has multiple closely-coupled effects with individual feedwater heaters in each effect. Feedwater manifolds in each effect supply feedwater to double fluted tubes through individual porcelain spray nozzles providing thin films on the tubes. The feedwater heaters are fed in series through each effect, while parallel branch lines supply the manifolds via in-line strainers with provisions for blow-down during normal operation if strainer blockage occurs.

BACKGROUND OF THE INVENTION This invention relates generally to multiple-effect thin film desalination plants and more particularly to a feedwater heating and strainer arrangement for such plants.

Multiple-effect thin film desalination or water distillation plants are known, wherein each effect utilizes vertical tubes adapted to evaporate feedwater on one surface of the tubes and to condense steam on the other surface of the tubes, both in thin films. One such apparatus wherein the several stages or effects are arranged in vertical fashion may be seen by reference to U.S. Pat. 3,481,835 issued to T. C. Carnavos on Dec. 2, 1969. Enhanced heat exchange characteristics may be further obtained by use of double fluted heat exchange surfaces as disclosed in U.S. Pat. 3,291,704 issued to G. E. Diedrich and C. W. Lotz, while distillation apparatus arrangements incorporating such surfaces are disclosed in U.S. Pat. 3,244,601 to G. E. Diedrich. All of the foregoing patents are assigned to the present assignee and are incorporated by reference herein.

The above Carnavos patent disclosed supplying raw feedwater serially through feedwater heaters in each succeeding effect, while branch lines from the feedwater heating line supplied the manifolds for each effect in parallel fashion.

The Carnavos patent ofiered some improvements over the serial-flow prior art arrangements which were deficient in that the foreign matter in the feedwater was cumulative as it was pumped serially from one effect to the next. Typical of the prior art are multiple-effect distillation plants, in which each effect is a vertical cylinder separately mounted and piped with a complex series of piping and pumps. Usually, the brine emerging from the sump of each effect is pumped as feedwater to the succeeding effect. This results in pluggage of feed nozzles in succeeding effects because of scale, rust flakes, sediment and so forth.

3,697,383 Patented Oct. 10, 1972 If it is desired to include strainers or filters in the feedwater line to prevent plugging of the feed nozzles, it is very desirable to having some means to clean the strainers in the event that they become clogged or plugged. It would further be desirable to have a means for cleaning the strainers without the necessity for shutting down the desalination plant.

Accordingly, one object of the present invention is to provide an improved feedwater heating and strainer arrangement for a multiple effect thin film distillation plant with improved means for heating and cleaning the feedwater.

Another object of the invention is to provide a strainer arrangement in such a plant which allows blow-down or cleaning of separate effects during operation of the plant.

DRAWING The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is an end view, showing one effect partly in section, of a vertical tube thin film desalination plant,

FIG. 2 is a horizontal elevation, partly in section, of the desalination plant,

FIG. 3 is a top view of the desalination plant,

FIG. 4 is an enlarged detail view of the feedwater manifold, spray nozzle and fluted tube, and

'FIG. 5 is an enlarged horizontal view in cross section of the preferred in-line strainer used in practicing the invention.

SUMMARY OF THE INVENTION Briefly stated, the invention is practiced by providing a plurality of feedwater heater loops disposed in the condensing chambers of successive vertical tube evaporator efiects and connected in series flow relationship. A plurality of feedwater supply lines are connected between successive feedwater heaters and lead to the respective feedwater manifolds via in-line strainers equipped with blow-down valves.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, an end view of the desalination plant is shown, partially in section. so as to indicate details typical of one effect or stage of a multiple effect plant. The various effects are longitudinally spaced along a cylindrical pressure vessel 1 which is divided into a condensing chamber 2 in the upper half and a separation chamber 3 in the lower half. Steam condenses on the outer fluted surface of vertical tubes 4 and is conducted by means such as inclined plate 5 to the side where it is removed through condensate removal pipes 6.

Feedwater is heated in the pipes of a two pass feedwater heater 7 and a controlled flow of feedwater is supplied through a branch line 8 and through an in-line strainer 9 to the top of a feedwater manifold 10. Feedwater in the manifold is supplied through individual spray nozzles 11 (see also FIG. 4) in a thinvfilm along the inner fluted surface of tubes 4 where it evaporates and the resulting steam passes into the lower separation chamber 3. Unevaporated brine falls into the bottom of the pressure vesssel 1 and is passed to the succeeding effect by brine loops 12.

Referring now to FIG. 2 of the drawing, a number of successively higher temperature effects or stages are indicated by reference numerals 14, 15, 16 and 17. It will be understood that any number of such effects may be employed which are economically practicable and that the stages are substantially identical in internal construction withthe possible exception of sizes and proportions which are adjusted as necessary for varying flow rates.

Referring to the internal details ,of effects 15 which is shown in cross section, it will be seen thatthe effects are thermally closely coupled to improved efliciency and reduce costs. This is done by means of simple vertical partition walls 18 separating the effects. Openings 18a permit the passage of vapor from each higher pressure effect to a lower pressure effect, from left to right. The brine loops 12 similarly conduct unevaporated brine toward the right around partition wall 18 while providing a pressure seal. Caps 12a deflect liquid downward and improve the efficiency of flashing steam.

A downwardly extending baflie plate 19 is spaced from divider wall 18 to forma passage leading toward opening 18A. A moisture separator element 20. in the passage removes any liquid from the steam as it passes into the next lower pressure effect.

Referring now to FIG. 3 of the drawing, the top view shows the feedwater heater and strainer arrangement for supplying the feedwater manifolds 10 v.of successive effects 14-17. Feedwater enters from the right through inlet pipe 21, having been previously treated and deaerated inv a manner which will be known to those skilled in the art of desalination plants. Pipe 21 is connected to the inlet of a two-pass feedwater heater 22 located in eflect 14.

A pipe 23 connects the outlet of feedwater heater 22 to the inlet offeedwater heater 24. In like manner, a pipe 25 leads to the inlet of feeder 26 in effect 16 and a pipe 27 leads from the outlet'of heater 26 to heater 28 in effect 17, etc. Thus the feedwater heaters 22, 24, 26, 28 are connected in series flow relationship.

In order to supply feedwater at successively higher temperatures to the feedwater manifolds 10, branch lines 30, 31, 32 are Td to respective pipes 23, 25, 27 and lead to in-line strainers 33, 34, 35 respectively. Orifice plates (see also FIG. are placed in the flange connections designated 36 to indicate the flow rate, while valves 37 are used to adjust the flow rate.

Reference to FIG. 4 shows the details of supplying feedwater to the individual vertical fluted tubes from feedwater manifold 10. One tube 4 is shown with its end engaged in a tube sheet 38, the remainder of such tubes being identical. Tube sheet 38 and an upward curved wall 39 are sealingly engaged to provide a feedwater chamber 40. Disposed in theupper end of each tube 4 is a porcelain spray nozzle of the tangential swirl type. The spray nozzles are submerged in liquid. Tangentially skewed inlet holes such as 11a meter entering feedwater and provide a swirl. The liquid is thrown outward on the depending nozzle lip 11b to be distributed on the inner wall of tube 4 in a thin film. Tube 4 is provided with inside and outside longitudinal protuberances 4a functioning in the manner described in the aforementioned Diedrich and Lotz Pat. 3,291,704 and Diedrich Pat. 3,244,601.

Reference now to FIG. 5 of the drawing shows the arrangement of the in-line strainer used in practicing the present invention. The strainer which is an enlarged detailed view of the strainer 9 shown in FIG. 1 is supplied with feedwater from a branch'line 8 through a bolted flange connection having an orifice plate 38 interposed therein. The body of strainer 9 comprises a cylindrical pipe section 39 forming two coaxial legs 39a and 39b with a T having a base connection 40 leading to the feedwater manifold 10. An end closure plate 41 closes off the end of the strainer and is provided with a blow-down valve 42. The blow-down valve is purposely located at the bottom edge of the strainer where the major portion of sediment collects. A cyindrical perforated strainer element 43 is coaxially spaced within pipe 39 by means of a spacer ring 43a clamped between a flange 44 and the closure plate 41 with suitable gasket. Coaxial alignment of strainer element 43 is maintained at the other end by means of a spacer washer 45 attached to the element. The element is longitudinally compressed against a sealing ring 46 attached to the inside of the pipe 39 to maintain a tight seal.

OPERATION From an overall thermodynamic cycle standpoint, the operation of the multiple-effect desalination plant shown is substantially the same as. that shown in the aforementioned Carnavos Pat. 3,481,835. However there are several important differences material to the present invention. First, the illustrated embodiment concerns a horizontal arrangement of effects, rather than a vertical arrangement of effects, wherein gravity-head is not a factor in assisting or impeding liquid flows. Both brineand the steam generated in each effect inside the fluted tubes are successively passed toward the right or lower temperature elfects, the steam through the divider wall openings and the brine through the pressure-sealing brine loops 12. Secondly, with respect to the feedwater heating and strainer arrangement of the present invention, feedwater enters at pipe 21 and is successively heated in feedwater heaters 22, 24, 26, 28 as it passes to the left in series-flow relationship between heaters.- At each effect, a metered flow of feedwater is passed through branch lines 30, 31, 32 to strainers 33, 34, 35.

As will be seen in the enlarged view of FIG. 5 for a typical strainer, the feedwater flow is metered by orifice 38 and flows into the interior of the perforated cylindrical element 43 where any impurities such as sludge, rust particles, etc. are retained. The filtered feedwater flows through T connection 40 into the top of feedwater manifold 10, and since it is clean, there is no tendency to plug the feed nozzles 11.

One of the primary advantages of the invention lies in the in-line arrangement of the strainer leading to the blow- 7 down valve 42. It will be seen that by opening the valve 42, a straight-through passage is aiforded so that the cylindrical element 43 can be cleared of any trapped foreign matter through the valve. As will be seen later in the description, this operation can be carried out without interference to the operation of the desalination plant.

Reference to FIG. 4 shows that the feedwater entering header 10 flows through the small ports 11a of the nozzles 11 and, since foreign matter has been moved by strainer element 43, there is less likelihood of the small nozzle ports 11a becoming plugged, and hence affecting operation of the plant.

Since the feedwater branch lines are connected in parallel to the feedwater heater line, it will be appreciated that any one of the branch lines may be blown down through valve 42 without materially affecting the operation of the plant. This offers a substantial advantage in desalination plants where the effects of corrosion products, rust, sediment and other deleterious substances are well known in the art.

While there has been described herein what is considred to be the preferred embodiment of the invention, it is of course understood that various other modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a. multiple-effect thin film desalination plant, each effect having a plurality of vertical tubes supplied from a feedwater manifold through nozzle means with ports subject to blockage by foreign matter in the feedwater, and wherein the feedwater manifolds are separately supplied from branch conduits in parallel flow relationship from a feedwater heater line, the improvement comprismg:

an in-line strainer connected between the branch conduit and the feedwater manifold for each of said effects, said strainer also having a blow-down valve on the upstream side of the strainer and adapted for discharging foreign matter therefrom without substantially shutting off the flow of feedwater to said manifold.

2. In a multiple-effect thin film desalination plant, each effect having a plurality of vertical tubes supplied from a feedwater manifold through nozzle means with ports subject to blockage by foreign matter in the feedwater, the improvement comprising:

a plurality of feedwater heaters, each one disposed in adjacent proximity to the vertical tubes of the same effects,

main conduit means connecting said heaters together in series flow relationship,

branch conduit means connected to said main conduit means between said feedwater heaters for extracting heated feedwater for each effect in parallel flow relationship,

strainer means connected between said branch conduit means and the feedwater manifold for each effect, said strainer means being adapted on its upstream side for discharging foreign matter therefrom without substantially shutting oi the flow of feedwater to said manifold.

3. The combination according to claim 2, wherein said strainer means comprises:

a T-shaped body member having a pair of coaxial legs and a base leg and having the base of the T connected to said feedwater manifold,

a perforated strainer element open at both ends disposed within and spaced from the walls of said coaxial legs,

a blow-down valve connected at one end of one coaxial leg of said T-section communicating with the inside of said strainer element, and

means connecting the other coaxial leg of said T-section to said branch conduit.

4. The combination according to claim 3, wherein said connecting means includes a flow-metering orifice disposed therein to meter the rate of flow to said feedwater manifold.

5. The combination according to claim 2, wherein said effects are horizontally disposed inside a longitudinal pressure vessel, said effects being closely coupled and separated only by partition walls.

6. The combination according to claim 5, wherein vapor flows successively through said effects through openings in said partition walls, over the exterior of said vertical tubes and said feedwater heater of each immediately downstream effect with respect to vapor flow.

7. The combination according to claim 5, wherein unevaporated feed water from said vertical tubes flows successively through said effects in vapor flow direction through brine loops beneath said partition Walls forming pressure seals between effects.

References Cited UNITED STATES PATENTS 1,843,242 2/1932 Rafton 210433 X 2,606,663 8/1952 Blackman et al. 210433 X 2,697,523 12/1954 Bloksma 210-433 X 3,099,607 7/1963 Lustenader et al. 203-10 3,532,152 10/1970 Cartinhour 15920 3,370,635 2/1968 Kumm 159-13 A FOREIGN PATENTS 1,132,096 6/1962 Germany 159-13 A NORMAN YUDKOFF, Primary Examiner I. SOFER, Assistant Examiner US. Cl. X.R.

159-.17, Dig. 8; 202-178, 236; 210-433 

